The present invention relates to a servo-amplifier for a multiaxis driving control system. More particularly this invention relates to a servo-amplifier with a communication interface for performing multi-drop communications in a multiaxis driving control system including RS232C by a personal computer or the like and a plurality of servo-amplifiers.
FIG. 6 shows a conventional type of multiaxis driving control system that performs multi-drop communications. This multiaxis driving control system comprises a RS232C communication medium 100 by a personal computer or the like that performs the main control over the communications, a converter 101 having a RS232C-compatible IC driver 101a and a RS422 (RS485)-compatible IC driver 101b. The converter 101 connects these IC drivers at a TTL level (IC voltage level) and converts the communication data from data for RS232C to data for RS422 (RS485). Further, this multiaxis driving control system has a plurality of servo-amplifiers 103 each having an RS422 (RS485) communication interface 102.
The RS232C communication medium 100 is connected to the IC driver 101a side of the converter 101 with an RS232C cable 104. On the other hand, the IC driver 101b side of the converter 101 is connected to the RS422 (RS485) communication interface 102 of the servo-amplifier 103 with an RS422 (RS485) cable 105. The servo-amplifiers 103 are cascaded to each other with the RS422 (RS485) cables 105. RS422 (RS485) communication is a communication that is realized by using a balanced IC driver that is compatible with the standards and being capable of 1-to-N communications characterized as balanced transmission.
A communication sequence of the above mentioned multiaxis driving control system will be explained here. Communications between RS232C communication medium 100 and the converter 101 are performed through RS232C. The converter 101 converts the data received trough RS232C to a communication format for RS422 (RS485) and executes communications with the servo-amplifiers 103. On the other hand, communications between the servo-amplifier 103 and the converter 101 is performed through RS422 (RS485). In this case, the converter 101 converts the data received through RS422 (RS485) to a communication format for RS232C and executes communications with the RS232C communication medium 100.
A communication packet used for the above mentioned communications is generally structured with a combination of a start bit, axis number (station number), command, data, and checksum. A multi-drop communication protocol in which the axis number of a target for communication is specified in the communication packet will be described herein.
As a technology related to the present invention, there are an interface module for communications of a programmable controller having a function of RS232C-RS422 -interconversion as disclosed in the Japanese Patent Laid-Open Publication No. HEI 3-251903 or a programmable controller having a serial communication port for RS232C and a serial communication port for RS422 for selectively using either one of the ports as disclosed in the Japanese Patent Laid-Open Publication No. HEI 6-110510.
In order to realize multi-drop communications in the above mentioned multiaxis driving control system, it is necessary that the multi-drop communication system has the RS422 (RS485) which is capable of performing 1-to-N communications. In addition, in order to realize communications with an RS232C communication medium as 1-to-1 communications, it is necessary to convert communication data for RS232C to communication data for RS422 (RS485) and also convert communication data for RS422 (RS485) to communication data for RS232C.
In order to perform the conversion of data as mentioned above, it is necessary to provide a dedicated converter as an additional unit in between an RS232C communication medium by a personal computer or the like and a servo-amplifier in the conventional communication systems. This results in an increase in the number of system components, which in turn reduces the transmission efficiency.
It is an object of the present invention to provide, for the purpose of solving the problems as described above, a servo-amplifier for a multiaxis driving control system with a communication interface enabling communications between an RS232C communication medium and a servo-amplifier through RS232C as well as enabling multi-drop communications to a plurality of servo-amplifiers through RS422 (RS485).
In the servo-amplifier for a multiaxis driving control system according to the present invention, the data received through communication with RS232C is fetched into a local station as well as the received data is converted into communication data for RS422 (RS485) and transmitted to other stations, then the data received through RS422 (RS485)-communication is converted into communication data for RS232C and transmitted to the other stations. Therefore, communication between a RS232C communication medium based on RS232C and a servo-amplifier and multi-drop communications to a plurality of servo-amplifiers with RS422 (RS485) can be performed without providing a dedicated converter.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.